Flight simulators are used by the military and civil-aviation industry as a low-cost alternative to actual flight time that allows pilots to gain valuable flight experience.
Although there are numerous devices used in flight simulation, all these devices can be categorized as non-motion and motion trainers.
Within the category of motion trainers, the most commonly known device is referred to as a Stewart Platform, a six DoF platform (“DoF”, pronounced as “doff” within the industry, means “degrees of freedom”), or hexapod platform. The six degrees of freedom are pitch, roll, yaw, heave, sway, and surge. This type of platform is a motion cueing device in that it gives the pilot the initial effect of a climb or dive, but due to limitations cannot replicate the complete flight envelope.
The other type of motion trainer is a Continuous G Device (CGD) which generally has the pitch, roll, and yaw degrees of freedom as well as planetary motion, hence the name Continuous G Device. A CGD is essentially a centrifuge-based simulator.
Over the years, a six DoF platform has become a standard, and is required for the so-called Level D flight simulator standard of civil aviation regulatory authorities such as the Federal Aviation Administration (FAA) in the United States and the European Aviation Safety Agency (EASA) in Europe. This type of platform-based-stationary trainer provides the trainee with an experience of being in an airplane cockpit with high-resolution, wide-field visual displays of flight scenes. These simulators also attempt to replicate motion cues through the use of a piston-driven-motion system located underneath the platform of the simulator. The pistons position the simulator's platform at different angles, which are usually limited in range of motion. For instance, such simulators cannot angle themselves beyond +/−45 degrees of pitch or +/−45 degrees of roll. They also do not have the capability to produce positive or negative G forces, to turn upside down, or to impart physiological stresses on the trainee.
A major drawback of such six DoF platform-based-stationary simulators, therefore, is that they cannot replicate a full 360 degree range of flight motion, nor impart Gravitational (G) forces on a pilot.
Unfortunately, most accidents resulting from a loss of airplane control in civil aviation—sometimes referred to as airplane “upsets”—involve airplane conditions outside the normal-flight envelope, such as pitch attitudes greater than 25 degrees nose up; pitch attitude greater than 10 degrees nose down; bank angles greater than 45 degrees; as well as increased G forces imparted on the flight crew. It is these airplane movements coupled with increased gravitational forces, which often causes disorienting vestibular and tactile stresses on a pilot during real-world-flight conditions.
Thus, even if a pilot learns the correct procedures for recovery from a loss-of-control situation such as an upset condition in an airplane, a pilot who is trained on only six DoF platform-based-stationary simulators may not be able to properly execute control of over an airplane in the real world, because he or she is not prepared to properly respond when confronted with the physiological stresses, external forces, and disorienting effects typically experienced by pilots during actual flight; especially flight conditions outside of the normal-flight envelope.
Centrifuge-based simulators, on the other hand, are generally able to provide trainees with all of the benefits of six DoF platform-based-stationary simulators, but are also able to replicate full-multi-axis movements (for pitch, roll or yaw) coupled with actual elevated G-forces through the use of planetary motion. Thus, centrifuge-based simulators are able to address deficiencies that platform-based-stationary simulators cannot replicate, such as placing elevated G-forces and physiological stresses on a pilot, while permitting the pilot to also experience unrestricted multi-axis movements associated with actual flight. This allows pilots to train to cope with physiological stresses during routine flight, and flight conditions outside of the normal-flight envelope.